Influence of Cr-doping on structural, magnetic and dielectric properties of M-type hexaferrites synthesized using microwave digestion technique

M-type hexaferrite SrCrxFe12-xO19 compounds doped with Cr (x=0, 1, 2, 3 and 4 at.%) were prepared by microwave digestion system. X-ray diffraction was used to study the structure and crystallization of the samples. The samples are found to have a hexagonal phase, SrFe12O19, as a main phase at 2Θ ≈ 33.144° and 35.618° for x = 0 and 1 respectively, and 32.451° and 34.295° for x ≥ 2. The Rietveld refined parameters such as the lattice parameters (a=b, c), direct and indirect cell volume, crystallite size and microstrain were investigated. TEM and SEM results showed that the samples have hexagonal shape and grain sizes range from 126 nm to 379 nm. Magnetization, M, as a function of the applied magnetic field, H, was obtained from the hysteresis loop. The coercive field, HC , saturation, Ms and remnant, Mr , magnetization and squareness ration, Mr/Ms , were extracted from the hysteresis loop results. These results revealed that HC is inversely proportional with the grains size of the samples but directly proportional with Cr-doping values candidating these compounds to be used in computer hard disk memories applications. M values are inversely proportional with Cr-doping values. The variation of conductivity, σ, impedance, Z, dielectric constant, ε, dielectric loss factor, tan δ and dissipation factor as functions of both AC frequency, F(Hz) and Cr-doping, x, were investigated. The maximum value of the dissipation factor was at x=2 which equals 8.05x109 m/F when F = 2x105 Hz. The impedance of the samples behaved as a capacitor reactance that makes our compounds candidate for many crucial dielectric applications.

Preparation and Characterization ZnO Nanorods for Photocatalyst Application

Zinc oxide (ZnO) nanorods are prepared onto glass substrates via chemical bath deposition method. ZnO nanoparticles is prepared onto glass substrate to act as a seed layer for grown ZnO NRs. Field Emission Scanning Electron Microscope (FESEM) image confirmed that the grown rods have hexagonal shape covered the surface of substrate. Further, the prepared ZnO NRs appeared good crystallinity according to X-ray diffraction method. The absorption edge for seeds nanoparticles layer appeared at wavelength of 362nm (3.42 eV) while it was at around 479nm (3.27 eV) nm for the grown ZnO NRs. The grown ZnO NRs showed two emission peaks at 381nm and 540nm corresponding to near band-to-band electron-hole recombination and oxygen vacancies, respectively. Degradation rate of methylene blue (MB) dye was 0.01% after 1h of illumination by UV light and increased to 71.4% after 4h of illumination.

Synthesis of SAPO-20 Using Isopropylamine as a Template from a SAPO-34 Precursor

SAPO-20 molecular sieve with the SOD framework was successfully synthesized using SAPO-34 as the precursor and isopropylamine (IPA) as the template by phase-transformation route. The influence of post-treatment time (in IPA, H2O, and SAPO-34 system) and NaOH concentration (in IPA, NaOH, H2O, and SAPO-34 system) on the products was investigated. The results showed that sheet debris SAPO-34 building the hollow-inside cubic morphologies which was padding with irregular SAPO-34. It was received for the as-synthesized spherical aggregation SAPO-20 with hexagonal shape when the ratio of n(OH-)/n (H2O) is 0.12 and the ratio of n(IPA)/n (H2O) is 0.07 in the synthesis gel. This method not only develops a new route for the synthesis of SAPO-20 molecular sieve, but also provides a way of using waste SAPO-34 catalyst, which can be used as a new exploration model for energy saving, consumption reduction and comprehensive utilization in SAPO-34 catalyst process.

On-Sun Testing of a High Temperature Solar Receiver's Flux Distribution

Concentrated solar power (CSP) is a promising technology in transitioning to renewable energy because of its abundance in nature and thermal energy storage capability. Among the four types of available CSP technology, including parabolic trough, linear Fresnel, power tower, and parabolic dishes, a power tower using a central receiver has more potential to generate high-temperature heat in a scale supporting power cycles efficiency and achieve low levelized cost of energy (LCOE). Other than the conventional type of receiver design, the high-absorptive receiver concept developed and presented in this paper is novel in its design approach. The novel receiver design originated from National Renewable Energy Laboratory (NREL) consists of an array of solar flux absorb tubes. The solar absorb tubes require uniform flux distribution and in-depth flux penetration through the three different reflective sections of tubes in a hexagonal shape. To evaluate this unique receiver design and thermal performance, the flux distribution, flux uniformity, and intensity were numerically simulated using ANSYS FLUENT and SolTrace modeling program. On-sun testing has been done at NREL high flux solar testing facility, based on the computational analysis.

Holes' Parameters Analysis of a Perforated Thin-Walled Lipped Beam Buckled Under a Bending Load

This work studied the effects of holes on the buckling characteristic of an open thin-walled lipped channel beam under a bending load. A nonlinear finite element method was utilised to examine the buckling behaviour of the beam. Experimental works were carried out to verify the finite element simulation. Three factors were chosen to examine their influence on the buckling of the beam. These factors namely, the holes’ shape, perforated ratio (hole length to beam height) and spacing ratio (centre to centre distance between holes to beam height). The finite elements output was analysed by implementing the Taguchi method to distinguish the best group of three parameters collections for optimal strength of buckling. Whereas the analysis of variance technique (ANOVA) method was applied to specify the impact of each parameter on critical buckling load. Outcomes showed that the combination of parameters that gives the best buckling strength is the hole with a hexagonal shape, perforated ratio =1.7 and spacing ratio =1.3, and the holes’ shape is the most effective factor. In addition, the study demonstrated that the hole's shape factor has the greatest influence on the buckling capacity. While the perforated ratio factor is the least influential.

Biosynthesis and Characterization of ZnO Nanoparticles Using Ochradenus arabicus and Their Effect on Growth and Antioxidant Systems of Maerua oblongifolia

Zincoxide nanoparticles (ZnO NPs) are among the most produced and used nanomaterials worldwide, and in recent times these nanoparticles have also been incorporate in plant science and agricultural research. The present study was planned to synthesize ZnO NPs biologically using Ochradenus arabicus leaves and examine their effect on the morphology and physiology properties of Maerua oblongifolia cultured in vitro. ZnO NPs were characterized by UV–visible spectroscopy (UV–vis), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy, which demonstrated hexagonal shape nanoparticles of size ranging from 10 to 50 nm. Thus, the study uncovered an efficient, eco-friendly and simple technique for biosynthesis of multifunctional ZnO NPs using Ochradenus arabicus following growth of Maerua oblongifolia shoots in different concentrations of ZnO NPs (0, 1.25, 2.5, 5, 10, or 20 mg L−1) in Murashige and Skoog medium. Remarkable increases in plant biomass, photosynthetic pigments, and total protein were recorded up to a concentration of 5 mg L−1; at the same time, the results demonstrated a significant reduction in lipid peroxidation levels with respect to control. Interestingly, the levels of proline and the antioxidant enzyme catalase (CAT), superoxide dismutase (SOD), and glutathione reductase (GR) activities were increased significantly in response to all ZnO NP treatments. These findings indicate that bioengineered ZnO NPs play a major role in accumulation of biomass and stimulating the activities of antioxidant enzymes in plant tissues. Thus, green-synthesized ZnO NPs might be of agricultural and medicinal benefit owing to their impacts on plants in vitro.

Dynamic Characterization of Microstructured Materials Made of Hexagonal-Shape Particles with Elastic Interfaces

This work aims to present the dynamic character of microstructured materials made of hexagonal-shape particles interacting with elastic interfaces. Several hexagonal shapes are analyzed to underline the different constitutive behavior of each texture. The mechanical behavior at the macro scale is analyzed by considering a discrete model assumed as a benchmark of the problem and it is compared to a homogenized micropolar model as well as a classical one. The advantages of the micropolar description with respect to the classical one are highlighted when internal lengths and anisotropies of microstuctured materials are taken into consideration. Comparisons are presented in terms of natural frequencies and modes of vibrations.